Method and apparatus for detecting relative positional deviation between two objects

ABSTRACT

Disclosed is a method and apparatus for detecting a relative positional deviation between first and second objects. In one preferred form of the invention, the detecting method includes the steps of (i) providing the first and second objects with diffraction gratings, respectively, each having a grating pitch larger than a wavelength of a light source used, (ii) placing the first and second objects so that a dielectric material layer having a thickness smaller than the wavelength of the light source used is interposed between the first and second objects, and so that the diffraction gratings of the first and second objects are opposed to each other, (iii) projecting light from the light source onto the diffraction gratings of the first and second objects, and (iv) detecting the relative positional deviation between the first and second objects on the basis of diffraction light projected from the diffraction gratings to a space.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to a method and an apparatus for detecting arelative positional deviation between two objects. More particularly,the invention concerns a technique for detecting a positional deviationvery precisely where a mold or a photomask to be used in near-fieldlithography or optical nanoimprint lithography should be aligned with asubstrate to be exposed or a workpiece to be processed.

In semiconductor exposure apparatuses, relative alignment of a mask or areticle with a wafer is carried out in various ways, and examples are amethod in which marker patterns on a mask or a reticle and on a waferare observed through a microscope optical system and a relativepositional deviation between them is detected by image processing, and amethod in which a mark or a reticle and a wafer are provided withdiffraction patterns, respectively, and a relative positional deviationbetween them is detected on the basis of interference of diffractionlights produced from lights incident on these diffraction gratings, asdiscussed by Flanders et al. in Appl. Phys. Lett. Vol. 31, p426 (1977).

On the other hand, the lithographic technology has been advanced anddiversified, and novel lithographic method have been proposed asemerging lithographic technology, such as step and flush imprintlithography (hereinafter, “optical nanoimprint lithography”) asdisclosed in U.S. Pat. No. 6,334,960, or near-field optical lithographyas disclosed in U.S. Pat. No. 6,171,730.

In accordance with such advanced lithographic methods, a pattern of asize of 100 nm or under can be produced. In these methods, a mold or aphotomask is brought into close proximity to a substrate to be exposedor a workpiece to be processed, to an order of 500 nm or under(typically, not greater than 200 nm), and the information that the moldor photomask bears is transferred to the substrate.

As regards relative alignment between a photomask or a mold with asubstrate to be exposed or a workpiece to be processed, in such advancedlithographic methods, a novel positional deviation detecting systemshould be provided to enable detection of a positional deviation moreprecisely while being adapted to a structure that the clearance betweenthe photomask or mold and the substrate to be exposed or workpiece to beprocessed is 500 nm or under.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide a methodand/or an apparatus for detecting a relative positional deviationbetween two objects more precisely.

In accordance with an aspect of the present invention, there is provideda method of detecting a relative positional deviation between first andsecond objects, said method comprising the steps of: providing the firstand second objects with diffraction gratings, respectively, each havinga grating pitch larger than a wavelength of a light source used; placingthe first and second objects so that a dielectric material layer havinga thickness smaller than the wavelength of the light source used isinterposed between the first and second objects, and so that thediffraction gratings of the first and second objects are opposed to eachother; projecting light from the light source onto the diffractiongratings of the first and second objects; and detecting the relativepositional deviation between the first and second objects on the basisof diffraction light projected from the diffraction gratings to a space.

In accordance with another aspect of the present invention, there isprovided an apparatus for detecting a relative positional deviationbetween first and second objects, said apparatus comprising: a lightsource having a predetermined wavelength; diffraction gratings providedon the first and second objects, respectively, each having a gratingpitch larger than the wavelength of the light source used, the first andsecond objects being disposed so that the diffraction gratings of thefirst and second objects are opposed to each other; a dielectricmaterial layer disposed between the first and second objects and havinga thickness smaller than the wavelength of the light source; anddetecting means for detecting diffraction light produced in response toprojection of light from the light source onto the diffraction gratingsof the first and second objects and for detecting the relativepositional deviation between the first and second objects on the basisof diffraction light projected from the diffraction gratings to a space.

In these aspects of the present invention, one of the first and secondobjects may be a photomask while the other may be a substrate to beexposed, and the dielectric material layer may be a photosensitivematerial layer.

Alternatively, one of the first and second objects may be an opticalnanoimprint mold while the other may be a substrate to be processed, andthe dielectric material layer may be a curing resin layer.

Briefly, in accordance with the present invention, a relative positionaldeviation detecting method and/or a relative positional deviationdetecting system by which a positional deviation between two objects canbe detected more precisely even in a structure wherein the two objectsare placed very close to each other with a clearance of 500 nm or under.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are schematic views, respectively, for explaining theprinciple of detecting a relative positional deviation between twoobjects, in an embodiment of the present invention.

FIG. 2 is a graph for explaining the relationship between a relativepositional deviation of two objects and a diffraction light intensity,in an embodiment of the present invention.

FIG. 3 is a schematic and diagrammatic view, showing a general structureof a relative positional deviation detecting system in a near-fieldlithography apparatus according to Example 1 of the present invention.

FIG. 4 is a schematic and diagrammatic view, showing a general structureof a relative positional deviation detecting system in an opticalnanoimprint lithography apparatus according to Example 2 of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the attached drawings.

Initially, the principle of detecting a relative positional deviationbetween two objects in the present invention will be explained withreference to FIGS. 1A-1C.

In FIGS. 1A-1C, a first object A (101) and a second object B (102) whichare the subjects of relative positional deviation detection are providedwith diffraction gratings A (103) and B (104), respectively. Each ofthese diffraction gratings A and B (103 and 104) has a grating pitch pwhich is made greater than the wavelength λ of light of a light source,to be described later. Furthermore, on the second object B (102), thereis a dielectric material thin film 105 which is formed with a thicknesssmaller than the wavelength of the light source used.

Here, the first object A (101) may be a mold in optical nanoimprintlithography or a photomask in near-field optical lithography, forexample. The second object B (102) may be a workpiece or substrate to beprocessed in optical nanoimprint lithography or a substrate to beexposed in near-field optical lithography, for example. In these cases,the dielectric material thin film 105 may be made of an ultraviolet-raysetting (curing) resin or a photoresist, for example.

The first object A (101) and the second object B (102) are disposed sothat, upon the upper surface of the dielectric material thin film 105,the diffraction gratings A (103) and B (104) of them are opposed to eachother. Here, the dielectric material thin film 105 is interposed betweenthe diffraction gratings A (103) and B (104), and these diffractiongratings are disposed with a clearance not greater than the wavelengthof light from the light source.

In operation, light (incident light) 106 having a wavelength λ from thelight source is incident on the diffraction gratings A (103) and B(104), and the light intensities of positive first (+1st) orderdiffraction light 107 and negative first (−1st) order diffraction light108 from the diffraction gratings A and B are measured. Here, since theclearance between the diffraction gratings A (103) and B (104) is madesmaller than the wavelength of incident light, as far as the incidentlight concerns, these diffraction gratings can serve as a singleintegral diffraction grating through the action of near-field light,being present adjacent the respective diffraction gratings, rather thantwo independent diffraction gratings.

In FIG. 1A, between the diffraction gratings A (103) and B (104), thereis no phase shift of diffraction gratings in the relative movementdirection (lateral direction as viewed in the drawing). Therefore, thepositive first (+1st) order diffraction light and the negative first(−1st) order diffraction light have the same intensity.

On the other hand, FIGS. 1B and 1C shows cases wherein the diffractiongrating B (104) has a rightward positional deviation and a leftwardpositional deviation with reference to the diffraction grating A (102),respectively. In these cases, there is a phase difference between thediffraction gratings A and B, such that, in relation to the incidentlight, the diffraction gratings A (103) and B (104) can serve, as aunit, as a diffraction grating having an asymmetric shape in lateraldirection, such as a blazed diffraction grating, for example. In thesecases, the positive first (+1st) order diffraction light 107 and thenegative first (−1st) order diffraction light have differentintensities. Thus, by measuring the difference in intensity, thedifference in phase between the diffraction gratings A (103) and B(104), namely, the relative positional deviation in lateral directionbetween the first object A (101) and the second object B (102) can bedetected.

FIG. 2 shows the relationship between the relative positional deviationamount and the diffraction light intensity change.

It is seen from FIG. 2 that, if the amount of relative positionaldeviation is zero, the positive first (+1st) order diffraction light andthe negative first (−1st) order diffraction light have the sameintensity, and that, in accordance with the relative positionaldeviation, the intensity of these diffraction lights changes. The periodof change is equal to the pitch p of the diffraction grating.

Next, specific examples of the present invention will be explained.

EXAMPLE 1

Example 1 is an embodiment wherein a detecting system of the presentinvention for detecting a relative positional deviation between twoobjects is applied to constitute a near-field lithography apparatus.

FIG. 3 shows a general structure of a relative positional deviationdetecting system incorporated into a near-field optical lithographyapparatus, according to this example.

In FIG. 3, a photomask 301 for near-field optical lithography isprovided with a left-hand side diffraction grating A (302) and aright-hand side diffraction grating C (303). A wafer 305 which is asubstrate to be exposed is coated with a photoresist 304 with athickness of 200 nm or under, and the wafer is provided with a left-handside diffraction grating B (306) and right-hand side diffraction gratingD (307). The diffraction gratings A and B (302 and 306) as well as thediffraction gratings C and D (303 and 307) are disposed close to eachother and opposed to each other with the photoresist 304 interposedtherebetween.

There are a laser A (308) and a laser B (309) which provide incidentlight A (310) and incident light B (311) both of a wavelength 635 nm.These incident lights A and B (310 and 311) from the lasers A and B areincident on the diffraction gratings A and B and the diffractiongratings C and D, respectively. Then, the intensity of negative first(−1st) order diffraction light 312 and the intensity of negative first(−1st) order diffraction light 313 are detected by using a photodetectorA (314) and a photodetector B (315), respectively. Thus, on the basis ofdetection signals produced by the photodetectors A and B (314 and 315),the amount of relative positional deviation between the photomask 301and the wafer 304 can be detected.

EXAMPLE 2

Example 2 is an embodiment in which a detecting system of the presentinvention for detecting a relative positional deviation between twoobjects is applied to constitute an optical nanoimprint lithographyapparatus.

FIG. 4 shows a general structure of a relative positional deviationdetecting system incorporated into an optical nanoimprint lithographyapparatus, according to this example.

In FIG. 4, a mold 401 for optical nanoimprint lithography is providedwith a left-hand side diffraction grating A (402) and a right-hand sidediffraction grating C (403). A wafer 405 which is a workpiece substrateto be processed is coated with an ultraviolet-ray setting resin liquid404 with a thickness of 200 nm or under, and the wafer is provided witha left-hand side diffraction grating B (406) and right-hand sidediffraction grating D (407). The diffraction gratings A and B (402 and406) as well as the diffraction gratings C and D (403 and 407) aredisposed close to each other and opposed to each other with the UVsetting resin 404 interposed therebetween.

There are a laser A (408) and a laser B (409) which provide incidentlight A (410) and incident light B (411) both of a wavelength 635 nm.These incident lights A and B (410 and 411) from the lasers A and B areincident on the diffraction gratings A and B and the diffractiongratings C and D, respectively. Then, the intensity of negative first(−1st) order diffraction light 412 and the intensity of negative first(−1st) order diffraction light 413 are detected by using a photodetectorA (414) and a photodetector B (415), respectively. Thus, on the basis ofdetection signals produced by the photodetectors A and B (414 and 415),the amount of relative positional deviation between the mold 401 and thewafer 404 can be detected.

Although this example has been explained with reference to a mold foroptical nanoimprint lithography and an UV setting resin, the concept ofthe present invention can be applied also to a system using ananoimprint lithography mold and a thermosetting resin, as disclosed inU.S. Pat. No. 5,772,905.

Although Examples 1 and 2 described above have been explained withreference to a case where one-dimensional diffraction gratings are used,the present invention is not limited to this. Two-dimensionaldiffraction gratings may be used, for example. As regards suchtwo-dimensional diffraction grating, a concentric diffraction gratingsuch as Fresnel zone plate may be used, for example. In that occasion,there would be an additional advantage that, as well as a periodicrelative positional deviation detection signal, an absolute positionaldeviation detection signal is obtainable.

Furthermore, although Examples 1 and 2 described above have beenexplained with reference to a case where diffraction lights fromleft-hand side and right-hand side pairs of diffraction gratings (A andB; and C and D) are detected respectively and the intensities of themare compared, it would be understood form FIGS. 3 and 4 that, byshifting the phase of the diffraction gratings, the peak position of thesignal from the paired diffraction gratings can be shifted. Thus, thestructure may be arranged appropriately to provide a detection systemsuitable to a required condition, such as differential detection type,for example.

In accordance with the embodiments and examples of the present inventionas described above, two objects whose relative positional deviation isgoing to be detected are provided with two diffraction gratings while adielectric material layer having a thickness smaller than the wavelengthof detection light is provided therebetween. The detection light isprojected to the diffraction gratings, and diffraction light from thesetwo diffraction gratings which serve like a single integral diffractiongrating through the action of near-field light being present adjacentthe diffraction gratings, is detected. On the basis of this, the amountof relative positional deviation between the two objects can be detectedvery precisely.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.2004-192252 filed Jun. 29, 2004, for which is hereby incorporated byreference.

1. A method of detecting a relative positional deviation between firstand second objects, said method comprising the steps of: providing thefirst and second objects with diffraction gratings, respectively, eachhaving a grating pitch larger than a wavelength of a light source used;placing the first and second objects so that a dielectric material layerhaving a thickness smaller than the wavelength of the light source usedis interposed between the first and second objects, and so that thediffraction gratings of the first and second objects are opposed to eachother; projecting light from the light source onto the diffractiongratings of the first and second objects; and detecting the relativepositional deviation between the first and second objects on the basisof diffraction light projected from the diffraction gratings to a space.2. A method according to claim 1, wherein the first and second objectsare provided with plural pairs of diffraction gratings, the diffractiongratings in each pair being disposed opposed to each other, and whereinlight from the light source is incident on the plural pairs ofdiffraction gratings and diffraction light projected from the pluralpairs of diffraction gratings to the space is detected.
 3. A methodaccording to claim 1, wherein each of the diffraction gratings is atwo-dimensional diffraction grating.
 4. A method according to claim 1,wherein one of the first and second objects is a photomask while theother is a substrate to be exposed, and wherein the dielectric materiallayer is a photosensitive material layer.
 5. A method according to claim1, wherein one of the first and second objects is an optical nanoimprintmold while the other is a substrate to be processed, and wherein thedielectric material layer is a curing resin layer.
 6. An apparatus fordetecting a relative positional deviation between first and secondobjects, said apparatus comprising: a light source having apredetermined wavelength; diffraction gratings provided on the first andsecond objects, respectively, each having a grating pitch larger thanthe wavelength of the light source used, the first and second objectsbeing disposed so that the diffraction gratings of the first and secondobjects are opposed to each other; a dielectric material layer disposedbetween the first and second objects and having a thickness smaller thanthe wavelength of the light source; and detecting means for detectingdiffraction light produced in response to projection of light from thelight source onto the diffraction gratings of the first and secondobjects and for detecting the relative positional deviation between thefirst and second objects on the basis of diffraction light projectedfrom the diffraction gratings to a space.
 7. An apparatus according toclaim 6, wherein the first and second objects are provided with pluralpairs of diffraction gratings, the diffraction gratings in each pairbeing disposed opposed to each other, and wherein light from the lightsource is incident on the plural pairs of diffraction gratings anddiffraction light projected from the plural pairs of diffractiongratings to the space is detected by said detecting means.
 8. Anapparatus according to claim 6, wherein each of the diffraction gratingsis a two-dimensional diffraction grating.
 9. An apparatus according toclaim 6, wherein one of the first and second objects is a photomaskwhile the other is a substrate to be exposed, and wherein the dielectricmaterial layer is a photosensitive material layer.
 10. An apparatusaccording to claim 6, wherein one of the first and second objects is anoptical nanoimprint mold while the other is a substrate to be processed,and wherein the dielectric material layer is a curing resin layer.